Integrated circuit structure incorporating an inductor, an associated design method and an associated design system

ABSTRACT

Disclosed are embodiments of a circuit (e.g., an electrostatic discharge (ESD) circuit), a design methodology and a design system. In the circuit, an ESD device is wired to a first metal level (e.g., M1). An inductor is formed in a second metal level (e.g., M5) above the first metal level and is aligned over and electrically connected in parallel to the ESD device by a single vertical via stack. The inductor is configured to nullify, for a given application frequency, the capacitance value of the ESD device. The quality factor of the inductor is optimized by providing, on a third metal level (e.g., M3) between the second metal level and the first metal level, a shield to minimize inductive coupling. An opening in the shield allows the via stack to pass through, trading off Q factor reduction for size-scaling and ESD robustness improvements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.11/692,948 filed Mar. 29, 2007, which has issued as U.S. Pat. No.7,750,408, the complete disclosure of which, in its entirety, is hereinincorporated by reference.

BACKGROUND

1. Field of the Invention

The embodiments of the invention generally relate to inductors and, moreparticularly, to an integrated circuit structure incorporating a backend of the line (BEOL) inductor.

2. Description of the Related Art

Circuit designers for radio frequency (RF) applications want a constantimpedance (Z_(RF)) (e.g., Z_(RF)=50 Ohms). Impedance (Z_(c)) of acapacitor is defined as one over the frequency (ω) capacitance (C)(i.e., Z_(c)=1/ωC). Thus, if a silicon device with load capacitance isadded to an RF application, then the added capacitance will necessarilydecrease impedance.

Electrostatic discharge (ESD) devices are often connected toInput/Output (I/O) pads of integrated circuits in order to safelydischarge electrostatic discharge current (e.g., from human body model(HBM) events, charged device model (CDM) events, machine model (MM)events, etc.). However, ESD devices are typically formed using activeelements, such as diodes, transistors, rectifiers, etc., whichinherently provide capacitance (C). Thus, incorporation of ESD devicesinto RF applications will, as discussed above, decrease the circuitimpedance Z_(RF).

SUMMARY

Disclosed herein are embodiments of an improved integrated circuitstructure (e.g., an electrostatic discharge (ESD) circuit structure)that incorporates an inductor, a design methodology for such an ESDcircuit structure and an associated design system.

Embodiments of the integrated circuit structure can comprise asubstrate, a first metal level (e.g., M1, M2, etc.) above the substrate,and at least one additional metal level above the first metal level(e.g., M2-Mx).

This integrated circuit structure can further comprise an inductor inone of the additional metal levels (e.g., M5) above the first metallevel, thereby forming a back end of the line (BEOL) inductor. Theinductor can be aligned over and be substantially parallel to thesubstrate. The inductor can comprise a planar conductive coil (e.g., acircular coil, a rectangular coil, an octagonal coil, etc.), having aninner end and an outer end. Additionally, a conductor (e.g., a viastack) can extend vertically from one end (i.e., a first end, e.g., aninner end) of the coil down to the first metal level or through thefirst metal level to a silicon region in the substrate.

The integrated circuit structure can further comprise a patternedconductive shield for minimizing any inductive coupling between thesubstrate and the inductor. This shield can be located in an additionalmetal level between the first metal level and the inductor (e.g., in M2,M3, Mx, etc.). To accommodate the conductor, the shield comprises anopening, which allows the conductor to extend vertically down to a lowermetal level (e.g., the first metal level) or to the substrate from theend of the coil.

The inductor alone can function as an electrostatic discharge (ESD)device for a functional circuit (e.g., for an additional integratedcircuit in a radio frequency (RF) application that is connected inparallel to the inductor and wired to the first metal level (e.g., toM1)). The inductor can also serve as a “shunt” to ground, or V_(DD)power supply. Specifically, the integrated circuit structure can furthercomprise an input/output pad and an additional circuit. A second end(e.g., an outer end) of the coil can be electrically connected to apositive supply voltage (Vdd) or ground (V_(SS)) and the first end(e.g., the inner end) of the coil can be electrically connected to theinput/pad and to the additional circuit (e.g., via the first metallevel). If the first end (e.g., the inner end) of the coil is furthershorted to ground and the coil comprises a metal wire having apredetermined minimum width that is capable of sustaining a specifiedcurrent density (e.g., an electrostatic discharge (ESD) current density)without failure, then the inductor can function as an ESD device.Alternatively, if the second end (e.g., the outer end) of the coil isfurther connected to V_(DD) and the coil comprises a metal wire having apredetermined minimum width that is capable of sustaining a specifiedcurrent density (e.g., an electrostatic discharge (ESD) current density)without failure, then the inductor can function as an ESD device.

Alternatively, the inductor can work in combination with another ESDdevice in an ESD circuit in order to provide ESD protection to thefunctional circuit. Specifically, in one exemplary embodiment, theintegrated circuit structure can comprise an electrostatic discharge(ESD) circuit. This ESD circuit can comprise a semiconductor deviceconnected in parallel with the BEOL inductor, and more specifically, anelectrostatic discharge (ESD) device connected in parallel with the BEOLinductor, for providing ESD protection to the functional circuit. Thus,the ESD circuit comprises a series inductor-capacitor (LC) circuitbecause the ESD device in the substrate necessarily has capacitance.

The inductor in this “LC” circuit can be configured to nullify, for agiven application frequency (ω), the capacitance value (C) of that ESDdevice. The embodiment further allows the size of the ESD circuit to beminimized and ESD robustness to be optimized by aligning the inductorabove the ESD device and using a single vertical conductor (e.g., a viastack) to form the electrical connection between an end of the inductorcoil (e.g., the inner end) and the ESD device. By placement of theinductor above the ESD device, area is saved (i.e., minimized) for theESD protection circuit. By connecting the inductor and ESD device with avertical conductor alone and avoiding the use of a horizontal underpass,ESD robustness can be improved. Additionally, the quality factor Q ofthe inductor is optimized by providing, between the inductor and ESDdevice, a shield to minimize inductive coupling. An opening in theshield allows the via stack to pass through, trading off a reduction inthe quality factor Q of the inductor with the gains in circuit sizescaling and ESD robustness.

More particularly, in this embodiment the integrated circuit structurecan comprise an additional circuit (e.g., a functional integratedcircuit for an RF application) electrically connected to an ESD circuit.That is, the integrated circuit can comprise a substrate, siliconregions of the ESD device and additional circuit in the substrate, andmultiple metal levels and inter-level dielectrics films above thesubstrate. The metal levels can comprise a first metal level (e.g., M1)above the substrate, and at least one additional metal level (e.g., M2,M3, M4, M5, Mx etc.) above the first metal level.

The ESD device can comprise a single component or a multi-componentdevice and can be electrically connected to a given metal level (i.e., afirst metal level, such as M1) above the substrate. The type and size ofthe ESD device can be predetermined so that the ESD device is capable ofproviding a desired level of electrostatic discharge (ESD) protection toan additional circuit (e.g., a integrated circuit designed for a radiofrequency (RF) application). The ESD device can, for example, be wiredto the first metal level (e.g., M1). Based on the size and type of theESD device, it will necessarily have a specific capacitance value.

This integrated circuit structure can further comprise an inductor inone of the additional metal levels (e.g., M5) above the first metallevel such that it is aligned over and substantially parallel to the ESDdevice. The inductor can comprise a planar conductive coil (e.g., acircular coil, a rectangular coil, an octagonal coil, etc.) having aninner end and an outer end. Additionally, a conductor (e.g., a viastack) can extend vertically from one end (i.e., a first end, e.g., theinner end) of the coil down to the metal level of the ESD device (e.g.,M1) or down to the substrate surface such that the inductor iselectrically connected to the ESD device metallization or directly tothe ESD device, respectively. Thus, the integrated circuit comprises anESD circuit comprising a parallel inductor-capacitor (LC) circuit.Connecting the inductor and ESD device with a vertical conductor aloneand avoiding the use of a horizontal underpass can improved ESDrobustness and can allow for ESD circuit size-scaling.

The coil can comprise a metal wire with a predetermined minimum widthcapable of sustaining a specified current density (e.g., a specifiedelectrostatic discharge (ESD) current density) without failure.Furthermore, the inductor in this LC circuit can be configured to have apredetermined inductance value (L). This predetermined inductance value(L) can be based on the capacitance value (C) of the ESD device and on aspecified application frequency (ω) (e.g., the specified applicationfrequency (ω) of the RF application). If the application frequency (ω)is equal to the resonance frequency of the LC circuit, the impedancevalue of the inductor-capacitor circuit (Z_(LC)) tends toward infinity.An LC circuit impedance value (Z_(LC)) at resonance frequency ensuresthat the LC circuit is insignificant when placed in parallel with thefunctional RF circuit (i.e., when placed in parallel with the additionalcircuit being protected by the ESD circuit so that the impedance valueof the additional circuit (Z_(RF)) is not decreased as a result of theESD device). This condition is optimal for functional circuits in RFapplications which require constant impedance. To accomplish this, theinductor should have an inductance value (L) that is approximately equalto one over the product of the capacitance value (C) of thesemiconductor device and the specified application frequency squared(ω²) (i.e., L=1/ω²C). Then, inductor is configured to achieve thatpredetermine inductance value (L). That is, the shape of the coil, thenumber of turns in the coil, the length of the coil and the diameter ofthe coil are all predetermined to achieve the predetermined inductancevalue (L) and to satisfy ESD robustness.

This embodiment can further comprise a shield in one of the additionalmetal levels between the ESD inductor and the first metal level (e.g.,in M2, M3 or M4) and, thus, between the inductor and the ESD device.This shield can be configured to minimize inductive coupling betweeninductor and ESD device and to ensure that the quality factor Q of theinductor is maximized. Additionally, this shield comprises an opening toaccommodate the conductor (e.g., the via stack) that extends between theinductor and the first metal layer or between the inductor and thesubstrate such that the ESD device and inductor are electricallyconnected. Although the opening in the shield may reduce the qualityfactor Q of the inductor, this reduction in quality factor is traded offagainst the size scaling and ESD robustness improvements.

In order to complete the ESD circuit and provide ESD protection to thefunctional circuit, as described above, the integrated circuit structureof this embodiment can also comprise an input/output pad. The first end(e.g., the inner end) of the inductor coil, the ESD device and thefunctional circuit are electrically connected to each other as well asto the input/pad. Additionally, the second end (e.g., the outer end) ofthe coil can be electrically connected to ground and the ESD device canfurther be electrically connected to a positive supply voltage.Alternatively, the second end (e.g., the outer end) of the coil can beelectrically connected to a positive supply voltage and the ESD devicecan be electrically connected to ground. In this fashion, they are in aparallel configuration during a.c. analysis.

Also disclosed are embodiments of a method for designing theelectrostatic discharge circuit, as described above, as well as aprogram storage device readable by computer and tangibly embodying aprogram of instructions executable by the computer to perform thismethod.

Specifically, the method embodiments comprise receiving user input,including design parameters for an electrostatic discharge circuit forprotecting an additional circuit of, for example, a radio frequency (RF)application. The design parameters for the ESD circuit can specify thatthe ESD circuit will comprise an ESD device electrically connected inparallel to an inductor so as to form a LC circuit because the ESDdevice necessarily provides capacitance. More specifically, the designparameters can include, but are not limited to, a specific type of ESDdevice to be used, the desired ESD device protection level and thesurvival objectives for the inductor (i.e., the current density (e.g.,the ESD current density) which the inductor should be able to sustainwithout failure). Also received is a specified application frequency(i.e., the application frequency for the circuit being protecting by theESD circuit).

Based on these design parameters, an initial design for the ESD devicealone is generated (i.e., a first design). This includes inter-leveldielectric films, and wiring of the ESD device (e.g., to a first metallevel, such as M1) above the ESD device silicon regions.

Based on this first design, a capacitance value for the ESD device canbe determined. Specifically, a table of capacitance values according todevice sizes and types can be accessed and the capacitance value of theESD device can thus be determined based on its type and size asspecified by the first design.

Once the capacitance value of the ESD device is determined, a desiredinductance value for the inductor can be determined so that the LCcircuit (i.e., the ESD circuit) has a resonant frequency at theapplication frequency. When the application frequency is at the LC tankresonant frequency, the LC ESD circuit will have an impedance value thatapproaches infinity. Specifically, an LC circuit impedance value(Z_(LC)) at resonant frequency ensures that the LC circuit parallelimpedance is large compared to the functional circuit being protected bythe ESD circuit so that the impedance value of the additional circuit(Z_(RF)) is not decreased as a result of the ESD device. This conditionis optimal for circuits in RF applications which require constantimpedance. Note that in this methodology, it is clear that the circuitdesigner can choose a LC value such that the desired net impedance isachieved for the given circuit application (e.g., the ESD device and Lcombination can be near the application frequency and have additionalimpedance contributions). To determine the inductance value (L) thedesign system solves for one over the product of the capacitance value(C) of the ESD device and the specified application frequency squared(ω²) (i.e., L=1/ω²C).

Once the inductance value (L) is determined, then another design (i.e.,a second design) can be generated which comprises an inductor with theinductance value previously determined and which also incorporates theinitial design for the ESD device. Specifically, the design for theinductor-ESD device combination (i.e., the second design) is generatedsuch that it comprises a planar conductive coil formed in a second metallevel (e.g., the M5 level) that is above the first metal level (e.g.,above M1) and, more specifically, that is above the ESD device.Achieving the desired inductance value is accomplished by selecting thediameter of the planar conductive coil, the shape of the coil, thenumber of turns in the coil and the length of the coil. This seconddesign should orient (i.e., align) the inductor over the ESD device andshould electrically connect the inductor to either the first metal level(e.g., M1) to which the ESD device is wired or to the substrate, suchthat the inductor and ESD device are electrically connected This isaccomplished by providing a conductor (e.g., a via stack) that extendsvertically from one end (i.e., a first end, e.g., the inner end) of theinductor coil to the first metal level (i.e., the ESD metallization,e.g., M1) or directly to the ESD device at the substrate surface suchthat the ESD device and inductor are electrically connected.

Additionally, as mentioned above, the design parameters received asinput from a user can comprise a specified current density (e.g., an ESDcurrent density), which the inductor should be able to sustain withoutfailure. Based on this current density, the method can further comprisedetermining the minimum wire width required for the inductor to be ableto sustain this current density and, then generating the second designso that the inductor coil has no less than this minimum wire width.

By designing the ESD circuit with both an ESD device and an inductorconnected in parallel, the net impedance of the RF circuit (i.e., thefunctional circuit being protected by the inductor-ESD circuit) remainsuniform (i.e., constant), which is optimal for RF applications. Bydesigning the ESD circuit with a vertical via stack and avoiding the useof a horizontal underpass, ESD robustness can be improved. By designingthe ESD circuit such that the inductor is positioned directly over theESD device and such that a via stack connects one end of the inductorcoil (i.e., the first end, e.g., the inner end) to the first metallevel, the area (e.g., the total size) of the ESD circuit can beminimized. That is, placing a silicon device (e.g. ESD silicon device)under the inductor does not waste the silicon area and placing theinductor over the ESD device does not waste area for the inductor area.Additionally, using an inductor in the ESD circuit instead of a secondsilicon element saves area on the chip surface. However, because the ESDdevice is positioned below the inductor, inductive coupling will occurand the quality factor Q of the inductor will be reduced. This can becompensated through RF design or introduction of other elements, such asmetal shields.

Therefore, the method embodiments further comprise generating a thirddesign comprising a shield in a third metal level (e.g., M3) between afirst metal level and a second metal level. This shield is placedbetween the inductive coil, and the metal levels of the ESD element. Thedesign for this shield can be configured to minimize inductive couplingbetween the inductor and the electrostatic discharge device of thesecond design. This shield can further be designed to include an openingto accommodate the conductor (e.g., the via stack) that extends betweenthe inductor and first metal level (e.g., M1) or the substrate surfacesuch that the ESD device and inductor are electrically connected. Whilethis opening may reduce the quality factor Q of the inductor to adegree, this reduction in quality factor is traded off against the ESDcircuit size-scaling gains as well as ESD circuit robustness.

The method embodiments, as described above, can be computer-implementedand can, for example, be accomplished by accessing a design kitcomprising hierarchical parameterized cells (p-cells) for electroniccomponents of electrostatic discharge devices, inductors and shields,each of which can be constructed in a computer-aided design (CAD)environment. Then, each of the designs (i.e., the first design for theESD device alone, the second design that incorporates an inductor intothe first design and the third design that incorporates a shield intothe second design) can be generated by a processor using thesehierarchical parameterized cells.

Finally, also disclosed are embodiments of an associated design system.Specifically, the design system embodiments comprise a user interface,at least one processor, a design kit and a storage device.

The user interface can be adapted to receive design parameters for anelectrostatic discharge (ESD) circuit for protecting an additionalcircuit (e.g., a circuit of a radio frequency (RF) application). Thedesign parameters for the ESD circuit can specify that the ESD circuitwill comprise an ESD device electrically connected in parallel to aninductor so as to form an LC circuit because the ESD device necessarilyhas capacitance. More specifically, the design parameters can include,but are not limited to, a specific type of ESD device to be used, thedesired ESD device protection level and the survival objectives for theinductor (i.e., the current density (e.g., the ESD current density)which the inductor should be able to sustain without failure). Alsoreceived is a specified application frequency (i.e., the applicationfrequency for the circuit being protecting by the ESD circuit).

The processor can be adapted to generate an initial design (i.e., afirst design) for the ESD device alone based on the design parameters(e.g., based on the specific type of ESD device to be used and thedesired ESD device protection level). The first design that is generatedby the processor can indicate the type and size of the ESD device andthe wiring for the ESD device. For example, the design can indicate thatthe ESD device is wired to a first metal level (e.g., to the M1 level).

The processor can further be adapted to determine, based on this firstdesign, a capacitance value for the ESD device. Specifically, the designsystem can further comprise a storage device comprising a table ofcapacitance values according to device sizes and types.

The processor can be adapted to access the table in order to determinethe capacitance value of the ESD device based on its particular size andtype as specified in the initial design.

The processor can further be adapted to determine, based on thiscapacitance value and on the application frequency specified by theuser, a desired inductance value for the inductor so that the LC circuit(i.e., the ESD circuit) will have an impedance value that approachesinfinity. Specifically, a parallel LC circuit impedance value (Z_(LC))wherein the application frequency is equal to the resonance frequencyensures that the LC circuit is not seen by the additional circuit beingprotected by the ESD circuit so that the impedance value of theadditional circuit (Z_(RF)) is not decreased as a result of the ESDdevice. This condition is optimal for circuits in RF applications whichrequire constant impedance (e.g. 50 Ohms). To determine the inductancevalue (L) the method solves for one over the product of the capacitancevalue (C) of the ESD device and the specified application frequencysquared (ω²) (i.e., L=1/ω²C).

The processor can further be adapted to generate another design (i.e., asecond design) which comprises an inductor with the inductance valuepreviously determined and which also incorporates the initial design forthe ESD device. Specifically, the processor can generate the design forthe ESD inductor-ESD device combination (i.e., the second design) bydesigning a planar conductive coil that will be formed in a second metallevel (e.g., M5) that is above the first metal level (e.g., M1). Theprocessor can generate this design by selecting the diameter of a planarconductive coil, the shape of the coil, the number of turns in the coiland the length of the coil so that the resulting inductor will achievethe desired inductance value. The processor can further be adapted togenerate this second design such that the inductor is oriented (i.e.,aligned) over the ESD device and electrically connected to either theESD metallization (i.e., a first metal level) or to the ESD device atthe substrate surface by a conductor (e.g., a via stack) that extendsvertically from one end (i.e., a first end, e.g., an inner end) of theinductor coil downward such that the ESD device and inductor areelectrically connected.

Additionally, as mentioned above, the design parameters received asinput from a user can comprise a specified current density (e.g., an ESDcurrent density), which the inductor should be able to sustain withoutfailure. The processor can be adapted to determine the minimum wirewidth required for the inductor to be able to sustain this currentdensity and can further generate the second design so that the inductorcoil has no less than this minimum wire width (i.e., to assign theinductor to a particular metal level in the layout in order to ensurethat the minimum wire width can be achieved). In this process, the widthof the planar conductive coil is wide enough to guarantee ESD robustnessby evaluation of the current density and self-heating effects in thecoil inductor itself.

In order to minimize inductive coupling between the inductor and the ESDdevice of the second design and, thereby, to optimize the quality factor(Q) of the inductor, the processor can also be adapted to generate athird design that comprises a shield and that incorporates the seconddesign. Specifically, the processor can be adapted to generate thedesign for the inductor-shield-ESD device combination (i.e., the thirddesign) so that a shield is positioned between the inductor and ESDdevice and so that this shield is configured to minimize inductivecoupling. This shield, as designed, can include an opening toaccommodate the conductor (e.g., the via stack) that extends downwardfrom the inductor.

The design system can further comprise a design kit. This design kit cancomprise hierarchical parameterized cells (p-cells or Pcells) forelectronic components of electrostatic discharge devices, inductors andshields, each of which can be constructed in a computer-aided design(CAD) environment. The processor can be adapted to access the kit and touse these hierarchical parameterized cells in generating each of theabove-described designs (i.e., the first for the ESD device along, thesecond design that incorporates an inductor into the first design andthe third design that incorporates a shield into the second design).

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments of the invention and numerous specific detailsthereof, are given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of theembodiments of the invention without departing from the spirit thereof,and the embodiments of the invention include all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 is a drawing illustrating a top view of an integrated circuit;

FIG. 2 is a drawing illustrating a cross-section view of the integratedcircuit of FIG. 1;

FIG. 3 is a drawing illustrating a top view of an embodiment of anintegrated circuit structure;

FIG. 4 is a drawing illustrating cross-section view of the integratedcircuit structure of FIG. 3;

FIG. 5 is schematic diagram illustrating the integrated circuitstructure of FIG. 3;

FIG. 6 is a drawing illustrating cross-section view of anotherembodiment of an integrated circuit structure;

FIG. 7 is schematic diagram incorporating structure of FIG. 6;

FIG. 8 is an alternative schematic diagram incorporating the structureof FIG. 6;

FIG. 9 is a flow diagram illustrating an embodiment of a designmethodology;

FIG. 10 is as schematic diagram illustrating an embodiment of a designsystem; and

FIG. 11 is a schematic representation of a computer system suitable foruse in implementing the design methodology and system as describedherein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

As mentioned, Electrostatic discharge (ESD) devices are often connectedto Input/Output (I/O) pads of integrated circuits in order to safelydischarge electrostatic discharge current (e.g., from human body model(HBM) events, charged device model (CDM) events, machine model (MM)events, etc.). However, ESD devices are typically formed using activeelements, such as diodes, transistors, rectifiers, etc., whichinherently provide capacitance. Thus, incorporation of ESD devices intoRF applications will, as discussed above, hinder RF circuit performanceby increasing impedance.

To solve this problem, an inductor can be incorporated into the ESDcircuit. Specifically, an inductor incorporated into an ESD circuit willnullify the increase in capacitance and, thereby, keep impedanceconstant. However, incorporation of an inductor into an integratedcircuit presents additional problems. First, due to the large arearequired for inductors, size scaling of RF applications is limited.Second, for an inductor to have a high quality factor (Q), inductivecoupling between the inductor and active elements in the substrate mustbe minimized. Inductive coupling can be minimized, for example, byforming the inductor such that it is not over any active elements in thesubstrate. Alternatively, inductive coupling can be minimized by formingair columns beneath the inductor (as illustrated in U.S. Pat. No.7,105,420 of Chan et al., issued on Sep. 12, 2006 and incorporatedherein by reference), or by forming a shield between the inductor andsubstrate (as illustrated in U.S. Pat. No. 6,833,603 of Park et al.,issued on Dec. 21, 2004).

For example, FIGS. 1 and 2 illustrate a top view and a cross-sectionview of an exemplary structure 100 incorporating a BEOL inductor 130 anda shield 120. The integrated circuit structure 100 comprises a back endof the line (BEOL) inductor 130 (e.g., patterned in the M5 layer).Inductive coupling between this inductor 130 and a conductive substrate110 (e.g., containing active devices) can reduce the quality factor Q ofthe inductor 130. This inductive coupling can be reduced if no devicesare formed under the inductor 130. Alternatively, inductive coupling canbe eliminated or at least minimized by incorporating into the structure100 a patterned conductive shield 120 (e.g., in the M2 layer) that islarger in area than the inductor 130 and that prevents the formation ofcircular currents which result in inductive coupling.

Either way the electrical connection between the inner end 131 of theinductor 130 coil and any other component in the structure 100 (e.g., adevice in the substrate, another metal level, etc.) is typicallyprovided by a via stack 141 which extends down to a metal level (e.g.,M3) and connects to a conductive underpass or additional wire 142 onthis metal level. The underpass 142 extends laterally beyond inductor130 so that it may be connected to any of the other metal levels. Forexample, if to avoid inductive coupling no devices are located in thesubstrate below the inductor, the underpass 142 will allow the inner end131 of the coil to be connected to components outside the lateralboundaries of the inductor 130. Alternatively, if a shield is used toavoid inductive coupling, the underpass 142 will allow a connection thatbypasses (i.e., is diverted around) the shield 120 and down to thesubstrate 110. However, this structure 100 presents limits with respectto size scaling as well as electrostatic discharge (ESD) robustness.

Specifically, since the electrical connection 141-142 from the inner end131 of the inductor 130 includes the underpass 141 on a different metallevel, multiple metal levels are required for inductor 130.Additionally, the underpass 142 is electrically connected to othercomponents outside the lateral boundaries of the inductor 130 and shield120. Thus, the area required for the integrated circuit 100 is evengreater than that for an already large inductor 130. Furthermore, if theinductor 130 functions as and ESD device or, alternatively, is to beincorporated into an electrostatic discharge (ESD) circuit, the ESDrobustness of the inductor 130 is limited by the wire width at itssmallest point. That is, the electrostatic discharge (ESD) currentdensity that the inductor 130 is able to sustain without failure is afunction of the smallest width of the coil wire. Since typically theBEOL metal levels (Mn-M1) progressively decrease in thickness towardsthe substrate 110, the thickness of the metal level (e.g., M3) in whichthe underpass 142 of the inductor 130 is formed effectively limits theESD robustness of the inductor 130.

In view of the foregoing, disclosed herein are embodiments of animproved integrated circuit structure (e.g., an electrostatic discharge(ESD) circuit structure) that incorporates an inductor, a designmethodology for such an ESD circuit structure and an associated designsystem.

Referring to the top and cross-section view of FIGS. 3 and 4 incombination, embodiments of the integrated circuit structure 200 cancomprise a substrate 210, a first metal level (e.g., M1) above thesubstrate 210, and a second metal level (e.g., M5) above the first metallevel. This integrated circuit structure 200 can further comprise aninductor 230 in the second metal level (i.e., a back end of the line(BEOL) inductor). The inductor 230 can be aligned over and besubstantially parallel to the substrate 210. The inductor 230 cancomprise a planar conductive coil (e.g., a circular coil, a rectangularcoil, an octagonal coil, etc.), having an inner end 231 and an outer end232.

More specifically, the inductor 230 can comprise a patterned conductivewire 233 that has a first end (e.g., an inner end). The wire 233 canwind (i.e., spiral, turn, etc.) in a rectangular, square, circular,octagonal, etc. coil around the first end 231 such that each turn,spiral, etc. is on the same horizontal plane and such that eachsuccessive turn around the inner end 231 has a greater diameter. Thus,the body of the wire 233 can surround the first end 231. The wire 233can further have a second end 232 (e.g., an outer end). This wire 233can lie in a first plane (e.g., the second metal level, M5) that isparallel to the substrate 210 and parallel to a second plane (e.g., thefirst metal level, M1) above the substrate 210.

Additionally, a conductor 241 (e.g., a via stack) can extend verticallyfrom one end 231 (i.e., a first end, e.g., the inner end) of the coildown to the first metal level (e.g., M1) or to the substrate surfacesuch that the conductor 241 is perpendicular to the inductor 230, to thefirst metal level (e.g., M1) and to the substrate 210.

The integrated circuit structure 200 can further comprise a third metallevel (e.g., M2) between the first metal level (e.g., M1) and the secondmetal level (e.g., M5). This third metal level (i.e., a third plane) cancomprise a patterned conductive shield 220 for minimizing any couplingand, specifically, to minimize any inductive coupling between thesubstrate 210 and the inductor 230 and, thereby, to ensure that thequality factor Q of the inductor 230 is optimized. This shield 220 cancomprise any conductive patterned shield suitable for minimizinginductive coupling. Specifically, the pattern of the conductive shield220 can comprise a conductive structure that lies in the second plane(e.g., the first metal level, M1) that is parallel to the inductor 230.The conductive shield 220 can comprise a radial pattern, a linearpattern, or any other suitable pattern comprising slots 222 (e.g.,dielectric filled-sections) between conductive portions of the shield220, which prevent circular currents from forming and, thereby, preventinductive coupling. For example, the circuit 200 can incorporate aconductive patterned shield similar to those disclosed in U.S. Pat. No.6,833,603 of Park et al. issued on Dec. 21, 2004 and incorporated hereinby reference.

However, the shield 220 of the present invention can further comprise anopening 221 to accommodate the conductor 241 (e.g., the via stack) thatextends downward from the inductor 230 perpendicular to the shield 220.The space within the opening 221 between the via stack 241 and theshield 220 can be filled with an inter level dielectric to ensure thatthe via stack 241 is isolated from the shield 220. While this opening221 may reduce the quality factor Q of the inductor 230 to a degree,this reduction in quality is traded off against circuit size scalinggains as well as ESD robustness gains resulting from the fact that theinductor 230 does not require a narrow underpass (e.g., see underpass142 of FIG. 1) in a metal level (e.g., M3) between the inductor 230 andshield 220 so that an inner end of the inductor 230 may be electricallyconnected to either the first metal level (e.g., M1) or the substratesurface and, thereby circuits or devices in the substrate.

Referring to FIG. 5, the inductor 230 alone can function as anelectrostatic discharge (ESD) device for an additional circuit 280(e.g., a functional integrated circuit for a radio frequency (RF)application) wired to the first metal level (e.g., M1). Specifically,the integrated circuit structure can further comprise an input/outputpad 260 and an additional circuit 280. A second end 232 (e.g., the outerend) of the coil 230 can be electrically connected to a positive supplyvoltage 251 and the first end 231 (e.g., the inner end) of the coil 230can be electrically connected to the input/pad 260 and to the additionalcircuit 280 (e.g., via the first metal level). If the first end 231 ofthe coil 230 is further shorted to ground 252 and the coil 230 comprisesa metal wire having a predetermined minimum width that is capable ofsustaining a specified current density (e.g., an electrostatic discharge(ESD) current density) without failure, then the inductor 230 canfunction as an ESD device for protecting the circuit 280. Alternatively,if the second end (e.g., the outer end) of the coil is further connectedto V_(DD) and the coil comprises a metal wire having a predeterminedminimum width that is capable of sustaining a specified current density(e.g., an electrostatic discharge (ESD) current density) withoutfailure, then the inductor can function as an ESD device.

Alternatively, the inductor 230 can work in combination with another ESDdevice forming an ESD circuit in order to provide ESD protection to anadditional circuit that is wired to the first metal level (e.g., to afunctional integrated circuit used in an RF application). Specifically,referring to FIG. 6, in one exemplary embodiment, the integrated circuitstructure 600 can comprise an electrostatic discharge (ESD) circuit.This ESD circuit can comprise a semiconductor device connected inparallel with the BEOL inductor 630, and more specifically, anelectrostatic discharge (ESD) device 611 connected in parallel with theBEOL inductor 630, for providing ESD protection to the additionalcircuit. Thus, the ESD circuit comprises a series inductor-capacitor(LC) circuit because semiconductor devices necessarily have capacitance.

The inductor 630 in this parallel LC circuit (i.e., the ESD circuit) canbe configured to nullify, for a given application frequency (ω), thecapacitance value of that ESD device 611. The embodiment further allowsthe size of the ESD circuit to be minimized and ESD robustness to beoptimized by aligning the inductor above the ESD device 611 and using asingle vertical conductor 641 (e.g., a via stack) to form the electricalconnection between the inner end 631 of the inductor coil 630 and theESD device 611. Specifically, by avoiding the use of a horizontalunderpass between the inductor 630 and first metal level (e.g., M1), ESDrobustness can be improved because the width of the conductor would notbe reduced. Additionally, the quality factor Q of the inductor 630 isoptimized by providing, between the inductor 630 and ESD device 611, ashield 620 to minimize inductive coupling. An opening in the shield 620allows the via stack 641 to pass through, trading off a reduction in thequality factor Q of the inductor 630 with the gains in circuit sizescaling and ESD robustness.

More particularly, integrated circuit structure 600 can comprise asubstrate 610, a first metal level (e.g., M1) above the substrate 610,and a second metal level (e.g., M5) above the first metal level. Theintegrated circuit structure 600 can further comprise an ESD device 611in the substrate 610 and wired to (i.e., electrically connected to), forexample, the first metal level (e.g., M1). This ESD device 611 cancomprise a single component or a multi-component device. The type andsize of the ESD device 611 can be predetermined so that the ESD device611 is capable of providing a desired level of electrostatic discharge(ESD) protection to an additional circuit (e.g., a integrated circuitdesigned for a radio frequency (RF) application). Specifically, the ESDdevice 611 can comprise a conventional ESD device, for example, a diode,a double diode, a poly-bound diode, an n-type field effect transistor(n-FET), a p-type field effect transistor (p-FET), a bipolar transistor,a silicon-controlled rectifier, a resistor, a varactor, etc., or anysuitable combination thereof. The ESD device can comprise, for example,silicon, silicon germanium, germanium, gallium arsenide, or indiumphosphide. Based on the size and type of the ESD device 611, it willnecessarily have a specific capacitance value (C).

The integrated circuit structure 600 can further comprise an inductor630 in the second metal level (e.g., M5) such that is aligned over andsubstantially parallel to the ESD device 610. This inductor 630 cancomprise a planar conductive coil contained within the single metallevel (e.g., M5), having an inner end 631 and an outer end 631. Theinductor 630 can comprise a planar conductive coil (e.g., a circularcoil, a rectangular coil, a square coil, an octagonal coil, etc.),having an inner end 631 and an outer end 632. More specifically, theinductor 630 can comprise a patterned conductive wire 633 that has afirst end (e.g., an inner end). The wire 633 can wind (i.e., spiral,turn, etc.) in a circular, square, rectangular, octagonal, etc. coilaround the first end 631 such that each turn, spiral, etc. is on thesame horizontal plane and such that each successive turn around theinner end 631 has a greater diameter. Thus, the body of the wire 633 cansurround the first end 631. The wire 233 can further have a second end232 (e.g., an outer end). This wire 633 can lie in a first plane (e.g.,the second metal level, M5) that is parallel to the substrate 610 andparallel to a second plane (e.g., the first metal level, M1) above thesubstrate 610.

Additionally, a conductor 641 can extend vertically downward from oneend (i.e., a first end, e.g., the inner end 631) of the coil to thefirst metal level (e.g., M1) or to the substrate surface such that theconductor 641 is perpendicular to the inductor 230 in the second metallevel (e.g., M5), to the first metal level (e.g., M1) and to thesubstrate 610 and such that the inductor 630 is electrically connectedto the ESD device 611. This conductor 641 can comprise, for example, aconventionally formed BEOL via stack (i.e., a stacked via pillar). BEOLvia stacks are typically formed with wirings of high conductivitymetallurgies on different metal levels (e.g., M1-M5) embedded in andinsulated from each other by inter level dielectrics (ILD) andinterconnected at desired points by metal filled via-studs. Thus, theintegrated circuit 600 comprises an ESD circuit comprising a parallelinductor-capacitor (LC) circuit.

The coil 630 can comprise a metal wire (e.g., a copper (Cu) or (Al) wirethat is pre-selected for ESD robustness) with a predetermined minimumwidth 635 (i.e., cross-section) also pre-selected for ESD robustness(i.e., preselected to sustain a specified current density (e.g., aspecified electrostatic discharge current density) without failure.Thus, since typically the back end of the line (BEOL) metal levels(Mn-M1) progressively decrease in thickness towards the substrate 610(i.e., towards the ESD device 611), the inductor coil 630 can be formedin a pre-selected one of the BEOL metal levels (e.g., in M5, asillustrated) in order to accommodate the required minimum wire width635. As with the inductor 641, the conductor 641 can comprise apredetermined cross-section that is capable of sustaining the specifiedcurrent density without failure.

Furthermore, the inductor 630 in this LC circuit can be configured tohave a predetermined inductance value (L). This predetermined inductancevalue (L) can be based on the capacitance value (C) of the ESD device611 and on a specified application frequency (ω) (e.g., the applicationfrequency (ω) of the RF application) so that the overall impedance value(Z_(LC)) of the LC circuit is at or near LC resonance (e.g., isapproaching infinity). An LC circuit impedance value (Z_(LC)) at or nearLC resonance (i.e., approaching infinity) ensures that the LC circuit isnot seen by the additional circuit being protected by the ESD circuit(e.g., a functional integrated circuit in an RF application). Thiscondition is optimal for circuits in RF applications which requireconstant impedance. To accomplish this, the inductor 630 should have aninductance value (L) that is approximately equal to one over the productof the capacitance value (C) of the ESD device 611 and the specifiedapplication frequency squared (ω²) (i.e., L=1/ω²C). Then, inductor 630is configured to achieve that predetermine inductance value (L). Thatis, the shape of the coil 630 (e.g., a circular, square, rectangular,octagonal, etc.), the number of turns (i.e., spirals) in the coil 630,the length of the coil 630 from the inner end 631 to the outer end 632and the diameter of the coil 630 are all predetermined to achieve thepredetermined inductance value (L).

As discussed above, by forming the ESD circuit 600 with both an ESDdevice 611 and an inductor 630, impedance value of the additionalcircuit in the RF application remains (Z_(RF)) remains constant. Aconstant impedance value (E.g., of approximately 50 Ohms) is desirablefor RF applications. Additionally, by placing the inductor 630 directlyover the ESD device 611 and by connecting the inductor 630 and ESDdevice 611 with a vertical conductor 641, the overall size of the ESDcircuit 600 (i.e., the area of a chip taken up by the ESD circuit) canbe minimized. By connecting the inductor and ESD device with a verticalvia stack and avoiding the use of a horizontal underpass, ESD robustnesscan be improved. However, because the ESD device 611 is directly belowthe inductor 630, inductive coupling necessarily occurs and the qualityfactor Q of the inductor 630 is reduced.

Therefore, the circuit 600 can further comprise a shield 620 in a metallevel (e.g., M2) between the inductor 630 and the first metal level(e.g., M1) above the ESD device 611 to minimize inductive coupling andto ensure that the quality factor Q of the inductor 630 is optimized.This shield 620 can comprise a conductive structure that lies in thesecond plane (e.g., the first metal level, M1) that is parallel to theinductor 630. The conductive shield 620 can further comprise anyconductive patterned shield suitable for minimizing inductive coupling.Specifically, the pattern of the conductive shield 620 can comprise aradial pattern, a linear pattern, or any other suitable patterncomprising slots 622 (e.g., dielectric-filled slots) between conductiveportions 623 of the shield 620. These slots 622 prevent circularcurrents from forming and, thereby, prevent inductive coupling. Forexample, the circuit 600 can incorporate a conductive patterned shieldsimilar to those disclosed in U.S. Pat. No. 6,833,603 of Park et al.issued on Dec. 21, 2004 and incorporated herein by reference.

However, the shield 620 of the embodiment can further comprise anopening 621 to accommodate the conductor 641 (e.g., the via stack) thatextends downward form the inductor 630. The space within the opening 621between the via stack 641 and the shield 620 can be filled with aninter-level dielectric to ensure that the via stack 641 is isolated fromthe shield 620. While this opening 621 may reduce the quality factor Qof the inductor 630 to a degree, this reduction in quality is traded offagainst the ESD circuit size-scaling gains as well as ESD robustnessgains. These gains result from the fact that the inductor 630 is aligneddirectly above the ESD device and does not require a narrow underpass inan metal level (e.g., M3) between the shield 620 and inductor 630 (e.g.,see underpass 142 of FIG. 1) in order to allow an electrical connectionbetween the inner end 631 of the inductor coil 630 and any other on-chipcomponents outside the lateral boundaries of the shield 620 and inductor630.

Referring to the schematic illustrations in FIGS. 7 and 8, in order tocomplete the ESD circuit 600 and provide ESD protection to an additionalintegrated circuit 680 (e.g., for an RF application), the integratedcircuit structure 600, as described above, can also comprise aninput/output pad 260. The one end (i.e., the first end, e.g., the innerend 631) of the inductor coil 630 and the ESD device 611 areelectrically connected to each other as well as to the input/pad 660 andto the additional circuit 680. Additionally, as illustrated in FIG. 6,the second end (e.g., the outer end 632) of the coil 260 can beelectrically connected to ground 652 (VSS) and the ESD device 611 can beelectrically connected to a positive supply voltage 651 (VDD).Alternatively, as illustrated in FIG. 7, the second end (e.g., the outerend 632) of the coil 630 can be electrically connected to a positivesupply voltage 651 (VDD) and the ESD device 611 can be electricallyconnected to ground 652 (VSS).

Referring to FIG. 9, also disclosed are embodiments of a method fordesigning the integrated circuit structure 600, described above andillustrated in FIG. 6, as well as a program storage device readable bycomputer and tangibly embodying a program of instructions executable bythe computer to perform this method.

Specifically, the method embodiments comprise receiving user input,including design parameters for an electrostatic discharge circuit forprotecting an additional circuit of, for example, a radio frequency (RF)application (802-804). The design parameters for the ESD circuit canspecify that the ESD circuit will comprise an ESD device 611 in asemiconductor substrate 610 and electrically connected in parallel to aback end of the line (BEOL) inductor 630 so as to form an LC circuitbecause the ESD device necessarily has capacitance. More specifically,the design parameters can include, but are not limited to, a specifictype of ESD device 611 to be used, the desired ESD device protectionlevel and the survival objectives for the inductor (i.e., the currentdensity (e.g., the ESD current density) which the inductor should beable to sustain without failure) (804). Specifically, the ESD device 611can be specified as a conventional single or multi-component ESD device,for example, a diode, a double diode, a poly-bound diode, an n-typefield effect transistor (n-FET), a p-type field effect transistor(p-FET), a bipolar transistor, a silicon-controlled rectifier, aresistor, a varactor, etc., or any suitable combination thereof. Alsoreceived is a specified application frequency (i.e., the applicationfrequency for the circuit being protecting by the ESD circuit) (803).

Based on these user-defined design parameters (e.g., based on thespecific type of ESD device 611 to be used and the desired ESD deviceprotection level) as well as additional previously established (i.e.,programmed) design parameters for the selected ESD device, an initialdesign for the ESD device 611 alone is generated (i.e., a first design)(806). Generation of the first design can comprise generating bothschematic and layout designs which indicate among other things the typeand size of the ESD device as well as the wiring for the ESD device(807). For example, the design can indicate that the ESD device 611 iswired to the first metal level (e.g., M1).

Based on this first design, a capacitance value (C) for the ESD device611 can be determined (808). Specifically, a table of capacitance valuesaccording to device sizes and types can be accessed and the capacitancevalue of the ESD device 611 can thus be determined based on its type andsize as specified by the first design (809).

Once the capacitance value (C) of the ESD device 611 is determined, adesired inductance value (L) for the inductor 630 can be determined) sothat the overall impedance value (Z_(LC)) of the LC circuit is at ornear LC resonance (e.g., is approaching infinity) (810). Specifically,if the application frequency is approximately equal to the resonancefrequency of the LC circuit, than a LC circuit impedance value (Z_(LC))approaches infinity. An LC circuit impedance value (Z_(LC)) at resonancefrequency (i.e., approaching infinity) ensures that the LC circuit isinsignificant when placed in parallel with the additional circuit beingprotected by the ESD circuit (i.e., is not seen by the additionalcircuit being protected by the ESD circuit) so that the impedance valueof the additional circuit (Z_(RF)) is not decreased as a result of theESD device. This condition is optimal for functional circuits in RFapplications which require constant impedance. To determine theinductance value (L) the method solves for one over the product of thecapacitance value (C) of the ESD device and the specified applicationfrequency squared (ω²) (i.e., L=1/ω²C) (811).

Once the desired inductance value (L) is determined, then another design(i.e., a second design) can be generated which comprises an inductor 630with the inductance value previously determined and which alsoincorporates the initial design for the ESD device 611 (812).Specifically, the design for the inductor-ESD device combination (i.e.,the second design) is generated such that it comprises a planarconductive coil 630 formed in a second metal level (e.g., the M5 level)that is above the first metal level (e.g., above M1) and, morespecifically, that is above the ESD device 611. Achieving the desiredinductance value is accomplished by selecting the diameter of the planarconductive coil, the shape (e.g., square, rectangular, circular,octagonal, etc.) of the coil, the number of turns (i.e., spirals) in thecoil and the length of the coil from the inner end 631 to the outer end632 (814).

Specifically, the inductor 630 can be designed as a wire 633 that winds(i.e., spiral, turn, etc.) in a circular, square, rectangular,octagonal, etc. coil around the first end 631 such that each turn,spiral, etc. is on the same horizontal plane and such that eachsuccessive turn around the inner end 631 has a greater diameter. Thus,the body of the wire 633 can surround the first end 631. The wire 233can further have a second end 232 (e.g., an outer end). This wire 633can lie in a first plane (e.g., the second metal level, M5) that isparallel to the substrate 610 and parallel to a second plane (e.g., thefirst metal level, M1) above the substrate 610.

This second design should orient (i.e., align) the inductor 630 over theESD device 611 and should electrically connect the inductor 630 toeither the first metal level (e.g., M1) or the substrate such that theinductor 630 and ESD device 611 are electrically connected. This isaccomplished by providing a conductor 641 that extends vertically fromone end (i.e., a first end, e.g., the inner end 631) of the inductorcoil 630 to the ESD device metallization (i.e., the first metal level(e.g., M1)) or to the substrate surface such that the conductor 641 isperpendicular to the inductor 230 in the second metal level (e.g., M5),to the first metal level (e.g., M1) and to the substrate 610 and suchthat the ESD device 611 and inductor 630 are electrically connected.This conductor 641 can be designed, for example, as a conventional BEOLvia stack (i.e., a stacked via pillar, see discussion above). By using asingle vertical via stack and avoiding the use of a horizontalunderpass, ESD robustness can be improved because the conductor widthdoes not have to be reduced.

Additionally, as mentioned above, the design parameters received asinput from a user at step 802 can comprise a specified current density(e.g., an ESD current density), which the ESD circuit and, particularly,the inductor 630 should be able to sustain without failure. Based onthis current density, the method can further comprise determining theminimum wire width required for the inductor 630 to be able to sustainthis current density (813) and, then generating the second design atprocess 812 so that the inductor coil 630 as well as the via stack 641have no less than this minimum wire width. In order to ensure that thisminimum wire width 635 is met by the inductor 630, the method comprisesselecting the metal level (e.g., M5) with the desired thickness forforming the coil. As with the first design, generation of the seconddesign can comprise generating both schematic and layout designs.

By designing the ESD circuit with both an ESD device 611 and an inductor630 in series, impedance (Z_(RF)) of the additional circuit beingprotected by the ESD circuit remains uniform (i.e., constant), which isoptimal for RF applications. By designing the ESD circuit such that theinductor 630 is positioned directly over the ESD device 611 and suchthat the electrical connection is provided by a vertical via stack 641,the size of the ESD circuit can be minimized. However, because the ESDdevice 611 is positioned directly below the inductor 630, inductivecoupling will occur and the quality factor Q of the inductor 630 will bereduced. Therefore, the method embodiments further comprise generating athird design comprising a patterned conductive shield 620 (816).

Generating the design for the inductor-shield-ESD device combination(i.e., the third design) can comprise designing a shield 620 that is tobe positioned parallel to and between the inductor 230 and ESD device210 and that is configured to minimize capacitance coupling (817). Thedesign for the shield 620 can comprise a conductive structure that liesin the second plane (e.g., the first metal level, M1) that is parallelto the inductor 630. Additionally, the design for the shield 620 cancomprise any conductive planar patterned shield suitable for minimizinginductive coupling. Specifically, the pattern of the conductive shield620 can comprise a radial pattern, a linear pattern, or any othersuitable pattern comprising slots 622 (e.g., dielectric-filled slots)between conductive portions 623 of the shield 620. These slots 622prevent circular currents from forming and, thereby, prevent inductivecoupling. For example, the circuit 600 can incorporate a conductivepatterned shield similar to those disclosed in U.S. Pat. No. 6,833,603of Park et al. issued on Dec. 21, 2004 and incorporated herein byreference.

However, the shield 620 can further be designed to include an opening621 to accommodate the conductor 641 (e.g., the via stack) that extendsdownward from the inductor 630. The design can further include aninter-level dielectric (ILD) material to fill the space in the opening621 surrounding the via pillar 641. While this opening 621 may reducethe quality factor Q of the inductor 630 to a degree, this reduction inquality is traded off against the ESD circuit size-scaling gains as wellas ESD circuit robustness gains, which result from the fact that theinductor 630 does not require a narrow underpass (see underpass 142 ofFIG. 1) to bypass the shield 620 and complete the electrical connectionbetween the inductor 630 and ESD device 611.

The method embodiments, as described above, can be computer-implementedin a manner similar to the method embodiments disclosed in the followingdocuments which are incorporated herein by reference: (1) U.S. Pat. No.6,704,179 of Voldman, issued on Mar. 9, 2004 and (2) U.S. PatentApplication Pub. No. 2005/0102644 of Collins et al., published on May12, 2005. Specifically, the method of designing the ESD circuit 600, asdescribed above, can be implemented at each of the design stages (i.e.,the first design stage for the ESD device alone (see step 802), thesecond design stage that incorporates an inductor into the first design(see step 812), and the third design stage that incorporates a shieldinto the second design (see step 816)), using a design kit comprisinghierarchical parameterized cells (p-cells), which are constructed intohigher level networks to ultimately form layout and schematic designsfor the completed ESD circuit 600.

More specifically, the design kit comprises hierarchical parameterizedcells or p-cells for electronic components of ESD devices, inductors andshields. The p-cells within the kit can comprise simple lower levelp-cells comprising the lowest level of components and higher levelp-cells comprising, for example, strings of components. These p-cellsare essentially computer models of the components comprising all of theparameters necessary for the computer to simulate the components inorder to generate both layout and schematic designs. Some of the p-cellparameters are fixed (e.g., by the type of component), while others areuser-specified or auto-generated based on user-inputs. Additionally,some of the p-cells can be manipulated (i.e., are grow-able usingstretch lines to adjust size, shape, etc.) in order to achieve certainparameters. The p-cells, as selected and manipulated, can be connectedwith parameterized interconnects to ultimately generate the ESD circuit200 layout and schematic.

Finally, referring to FIG. 10, also disclosed are embodiments of anassociated design system 900 for designing the electrostatic dischargecircuit 200, described above and illustrated in FIGS. 3 and 5.Specifically, the design system 900 embodiments comprise a userinterface 910, at least one processor 920, a design kit 930 and astorage device 940.

The user interface 910 (e.g., a graphical user interface (GUI)) can beadapted to receive design parameters for an electrostatic discharge(ESD) circuit for protecting an additional circuit (e.g., a circuit of aradio frequency (RF) application). The design parameters for the ESDcircuit can specify that the ESD circuit will comprise an ESD device 611in a substrate 610 and electrically connected in parallel to a BEOLinductor 630 so as to form an LC circuit. More specifically, the designparameters can include, but are not limited to, a specific type of ESDdevice to be used, the desired ESD device protection level and thesurvival objectives for the inductor (i.e., the current density (e.g.,the ESD current density) which the inductor should be able to sustainwithout failure). The ESD device 611 can be specified as a conventionalsingle or multi-component ESD device, for example, a diode, a doublediode, a poly-bound diode, an n-type field effect transistor (n-FET), ap-type field effect transistor (p-FET), a bipolar transistor, asilicon-controlled rectifier, a resistor, a varactor, etc., or anysuitable combination thereof. Also received is a specified applicationfrequency (i.e., the application frequency for the circuit beingprotecting by the ESD circuit).

The processor 920 can be adapted to (e.g., programmed) to generate aninitial design (i.e., a first design 951) for the ESD device 611 alonebased on the design parameters (e.g., based on the specific type of ESDdevice to be used and the desired ESD device protection level) receivedvia the user interface 910. Specifically, the ESD device 611 can bedesigned as conventional single or multi-component ESD device 611, forexample, a diode, a varactor, a poly-bound diode, an n-type field effecttransistor (n-FET), a p-type field effect transistor (p-FET), a bipolartransistor, a silicon-controlled rectifier, a resistor, etc. or anysuitable combination thereof (e.g., the double diode ESD device, asillustrated in FIG. 4). The first design 951 that is generated by theprocessor 920 can comprise both schematic and layout designs and canindicate the type and size of the ESD device 210.

The processor 920 can further be adapted to determine, based on thisfirst design 951, a capacitance value for the ESD device 611.Specifically, the design system 900 can further comprise a storagedevice 940 comprising a table 941 of capacitance values according todevice sizes and types. The processor 920 can be adapted to access thetable 941 in order to determine the capacitance value of the ESD device611 based on its particular size and type as specified in the initialdesign 951.

The processor 920 can further be adapted to determine, based on thiscapacitance value and on the application frequency specified by theuser, a desired inductance value for the inductor 630. The desiredinductance value for the inductor 630 can be determined so that the LCcircuit (i.e., the ESD circuit) will have an impedance value near itsresonant frequency. Specifically, an LC circuit impedance value (Z_(LC))near the resonant frequency (e.g., of approximately infinity) ensuresthat the LC circuit is not seen by the additional circuit beingprotected by the ESD circuit so that the impedance value of theadditional circuit (Z_(RF)) is not decreased as a result of the ESDdevice. This condition is optimal for circuits in RF applications whichrequire constant impedance. To determine the inductance value (L) forthe inductor 630, processor 920 is adapted to solve for one over theproduct of the capacitance value (C) of the ESD device 611 and thespecified application frequency squared (ω²) (i.e., L=1/ω²C).

The processor 920 can further be adapted to generate another design(i.e., a second design 952) which comprises an inductor 630 with theinductance value previously determined and which also incorporates theinitial design 951 for the ESD device 611 alone.

Specifically, the processor 920 can generate the design for theinductor-ESD device combination (i.e., the second design) by designing aplanar conductive coil 630 that will be formed in a second metal level(e.g., M5) above the first metal level (e.g., M1) to which the ESDdevice 611 is wired. The processor 920 can generate this design byselecting the diameter of a planar conductive coil 630, the shape (e.g.,rectangular, square, circular, octagonal, etc.) of the coil 630, thenumber of turns (i.e., spirals) in the coil 630 and the length of thecoil 630 from the inner end 631 to the outer end 632 so that theresulting inductor 630 will achieve the desired inductance value.Specifically, the inductor 630 can be designed by the processor 920 as awire 633 that winds (i.e., spiral, turn, etc.) in a circular, square,rectangular, octagonal, etc. coil around the first end 631 such thateach turn, spiral, etc. is on the same horizontal plane and such thateach successive turn around the inner end 631 has a greater diameter.Thus, the body of the wire 633 can surround the first end 631. The wire233 can further have a second end 232 (e.g., an outer end). This wire633 can lie in a first plane (e.g., the second metal level, M5) that isparallel to the substrate 610 and parallel to a second plane (e.g., thefirst metal level, M1) above the substrate 610.

The processor 920 can further be adapted to generate this second designsuch that the inductor 930 is oriented (i.e., aligned) over the ESDdevice 611 and electrically connected to the first metal level (e.g., M1to which the ESD device 611 is wired) by a conductor 641 (e.g., a viastack, as discussed above) that extends vertically from one end (i.e., afirst end, e.g., an inner end 631) of the inductor coil 630 to the ESDmetallization (i.e., the first metal level (e.g., M1)) or to thesubstrate surface such that the conductor 641 is perpendicular to theinductor 630 in the second metal level, to the first metal level and tothe substrate and such that the ESD device 611 and inductor 630 areelectrically connected.

Additionally, as mentioned above, the design parameters received asinput 910 from a user can comprise a specified current density (e.g., anESD current density), which the ESD circuit and, particularly, theinductor 630 should be able to sustain without failure. The processor920 can be adapted to determine the minimum wire width 635 required forthe inductor 630 to be able to sustain this current density and canfurther generate the second design 952 so that the inductor coil 630 andthe via stack 641 have no less than this minimum wire width 635. Thus,the processor 920 must assign the inductor 630 to a particular metallevel (e.g., M5) in the layout in order to ensure that the minimum wirewidth 635 can be achieved. As with the first design 951, this seconddesign 952 can be generated so that it comprises both schematic andlayout designs.

In order to minimize inductive coupling between the inductor 630 and theESD device 611 of the second design 952 and, thereby, to optimize thequality factor (Q), the processor 920 can also be adapted to generate athird design 953 that comprises a shield and that incorporates thesecond design 952. Specifically, the processor 920 can be adapted togenerate a design 953 for an inductor-shield-ESD device combination(i.e., a third design), wherein the shield is parallel to the inductor630 and the substrate. The design for the shield 620 can comprise anyplanar conductive patterned shield suitable for minimizing inductivecoupling. Specifically, the pattern of the conductive shield 620 cancomprise a radial pattern, a linear pattern, or any other suitablepattern comprising slots 622 (e.g., dielectric-filled slots) betweenconductive portions 623 of the shield 620. As discussed above, theseslots 622 prevent circular currents from forming and, thereby, preventinductive coupling.

The design system 900 can further comprise a design kit 930. This designkit 930 can be similar to that described in U.S. Pat. No. 6,704,179 andU.S. Patent Application Pub. No. 2005/0102644 referenced above.Specifically, this design kit 930 can comprise hierarchicalparameterized cells (p-cells) 931 for electronic components ofelectrostatic discharge devices, inductors and shields, each of whichcan be constructed in a computer-aided design (CAD) environment. Theprocessor 900 can be adapted to access the kit 930 and to use thesehierarchical parameterized cells in generating each of theabove-described designs (i.e., the first design 951 for the ESD device611 alone, the second design 952 that incorporates an inductor 630 intothe first design 951 and the third design 953 that incorporates a shield620 into the second design 951) at each of the design stages (see steps806, 812 and 816 of FIG. 9).

More specifically, the p-cells 931 within the design kit 930 cancomprise simple lower level p-cells comprising the lowest level ofcomponents for the different features of the ESD circuit (i.e., of ESDdevices, inductors and shields) and higher level p-cells comprising, forexample, strings of these components. These p-cells 931 are essentiallycomputer models of the one or more components with all of the parametersnecessary for the computer to simulate the component(s) in order togenerate both layout and schematic designs at each of the design stages.Some of the p-cell parameters are fixed (e.g., by the type ofcomponent), while others are user-specified or auto-generated based onuser-inputs. Additionally, some of the p-cells can be manipulated (i.e.,are grow-able using stretch lines to adjust size, shape, etc.) in orderto achieve certain parameters. The p-cells, as automatically selectedand manipulated, can be connected with parameterized interconnects toultimately generate the ESD circuit layout and schematic.

The method and system embodiments of the invention can each take theform of an entirely hardware embodiment, an entirely software embodimentor an embodiment including both hardware and software elements. Oneexemplary embodiment is implemented in software, which includes but isnot limited to firmware, resident software, microcode, etc.

Furthermore, these embodiments can take the form of a computer programproduct accessible from a computer-usable or computer-readable mediumproviding program code for use by or in connection with a computer orany instruction execution system. For the purposes of this description,a computer-usable or computer readable medium can be any apparatus thatcan comprise, store, communicate, propagate, or transport the programfor use by or in connection with the instruction execution system,apparatus, or device. The medium can be an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system (orapparatus or device) or a propagation medium. Examples of acomputer-readable medium include a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk and an opticaldisk. Current examples of optical disks include compact disk-read onlymemory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor connected directly orindirectly to memory elements through a system bus. The memory elementscan include local memory employed during actual execution of the programcode, bulk storage, and cache memories which provide temporary storageof at least some program code in order to reduce the number of timescode must be retrieved from bulk storage during execution.

Input/output (I/O) devices (including but not limited to keyboards,displays, pointing devices, etc.) can be connected to the system eitherdirectly or through intervening I/O controllers. Network adapters mayalso be connected to the system to enable the data processing system tobecome connected to other data processing systems or remote printers orstorage devices through intervening private or public networks. Modems,cable modem and Ethernet cards are just a few of the currently availabletypes of network adapters.

A representative hardware environment for practicing the embodiments ofthe invention is depicted in FIG. 11. This schematic drawing illustratesa hardware configuration of an information handling/computer system inaccordance with the embodiments of the invention. The system comprisesat least one processor or central processing unit (CPU) 10. The CPUs 10are interconnected via system bus 12 to various devices such as a randomaccess memory (RAM) 14, read-only memory (ROM) 16, and an input/output(I/O) adapter 18. The I/O adapter 18 can connect to peripheral devices,such as disk units 11 and tape drives 13, or other program storagedevices that are readable by the system. The system can read theinventive instructions on the program storage devices and follow theseinstructions to execute the methodology of the embodiments of theinvention. The system further includes a user interface adapter 19 thatconnects a keyboard 15, mouse 17, speaker 24, microphone 22, and/orother user interface devices such as a touch screen device (not shown)to the bus 12 to gather user input. Additionally, a communicationadapter 20 connects the bus 12 to a data processing network 25, and adisplay adapter 21 connects the bus 12 to a display device 23 which maybe embodied as an output device such as a monitor, printer, ortransmitter, for example.

Therefore, disclosed above are embodiments of an improved integratedcircuit structure and, particularly, an improved electrostatic discharge(ESD) circuit structure, which incorporates an inductor. Also, disclosedare a design methodology and a design system. The ESD circuit structurecan comprise an ESD device in a semiconductor substrate and wired to ametal level (e.g., M1, M2, M3, etc.) above the substrate. An inductor ina higher metal level (e.g., M5) can be aligned over and electricallyconnected in parallel to the ESD device by a via stack that extendsvertically from, for example, an inner end of the inductor coil down tothe given metal level (e.g. or to the silicon substrate). Thisconfiguration forms an inductor-capacitor (LC) ESD circuit and allowsfor ESD circuit size-scaling. Additionally, the inductor in the LCcircuit is configured to nullify, for a given application frequency, thecapacitance value of that ESD device. The quality factor Q of theinductor is optimized by providing, between the inductor and the ESDelement, a shield to minimize inductive coupling. An opening in theshield allows the via stack to pass through, trading off any reductionin the Q factor with gains in size-scaling and ESD robustness.

It is understood that in this methodology, the definition of theinductor, and any ESD element can be further expanded for co-synthesiswith the RF circuit, or part of the RF circuit or in parallel with theRF circuit. In addition, the methodology can be applied to more complexESD networks wherein the ESD inductor-ESD device LC parallel combinationcan be integrated with other ESD elements (e.g. diode and ESDinductor/ESD element series configuration) in series configurations.

It is understood that in this methodology, the definition of theinductor, and any ESD element can be further expanded for co-synthesiswith the RF circuit, or part of the RF circuit or in parallel with theRF circuit. In addition, the methodology can be applied to more complexESD networks wherein the ESD inductor-ESD device LC parallel combinationcan be integrated with other ESD elements (e.g. diode and ESDinductor/ESD element series configuration) in both parallelconfigurations.

It is understood that in this methodology, the definition of theinductor, and any ESD element can be further expanded for co-synthesiswith the RF circuit, or part of the RF circuit or in parallel with theRF circuit and not electrically connected to the VDD or VSS power rails.This methodology can be applied to both internal and external circuitswhere ESD robustness is desired within a peripheral circuit, or internalcircuit. In addition, this can be applied between power supplies (e.g.VDD to VSS), or between common ground (VSS to AVSS).

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, those skilled in the artwill recognize that the embodiments of the invention can be practicedwith modification within the spirit and scope of the appended claims.

1. A computer-implemented method for designing an integrated circuitstructure, said method comprising: receiving, by a computer, designparameters for an electrostatic discharge circuit and a specifiedapplication frequency, wherein said electrostatic discharge circuitcomprises an electrostatic discharge device electrically connected inparallel to an inductor; generating, by said computer, a first designfor said electrostatic discharge device based on said design parameters;determining, by said computer and based on said first design, acapacitance value for said electrostatic discharge device; determining,by said computer and based on said capacitance value and saidapplication frequency, an inductance value for said inductor to ensurethat a subsequently designed inductor-capacitor (LC) circuit will have aresonant frequency at said application frequency; and generating, bysaid computer, a second design comprising said inductor with saidinductance value aligned over and electrically connected to saidelectrostatic discharge device of said first design to form saidinductor-capacitor circuit.
 2. The method of claim 1, wherein saiddetermining of said capacitance value comprises: accessing a table ofcapacitance values according to device sizes and types; and determiningsaid capacitance value based on a type and size of said electrostaticdischarge device as specified by said first design.
 3. The method ofclaim 1, wherein said determining of said inductance value comprisessolving for one over a product of a capacitance value of saidelectrostatic discharge device and said specified application frequencysquared.
 4. The method of claim 1, wherein said generating of saidsecond design comprises selecting a diameter of a planar conductive coilfor said inductor, a shape of said coil, a number of turns in said coiland a length of said coil sufficient to achieve said inductance value.5. The method of claim 1, wherein said receiving of said designparameters comprises receiving a specified current density, and whereinsaid method further comprises: determining, by said computer, a minimumwire width for said inductor that is sufficient to sustain saidspecified current density without failure; and generating, by saidcomputer, said second design so that said inductor has no less than saidminimum wire width.
 6. The method of claim 1, wherein said generating ofsaid first design comprises generating said first design such that saidelectrostatic discharge device is wired to a first metal level abovesaid electrostatic discharge device, wherein said generating of saidsecond design comprises generating said second design such that saidinductor comprises a planar conductive coil in a second metal levelabove and parallel to said first metal level and such that a first endof said coil is electrically connected to said first metal level by aconductor extending vertically from said first end to said first metallevel such that said conductor is perpendicular to said inductor.
 7. Themethod of claim 6, further comprising generating, by said computer, athird design comprising a shield in a third metal level between andparallel to said first metal level and said second metal level, whereinsaid shield is configured to minimize inductive coupling between saidinductor and said electrostatic discharge device of said second designand comprises an opening through which said conductor extendsperpendicular to said shield.
 8. The method of claim 1, wherein saidgenerating of said first design, said generating of said second designand said generating of said third design comprise using a design kitcomprising hierarchical parameterized cells for electronic components ofelectrostatic discharge devices, inductors, and shields.
 9. A programstorage device readable by computer and tangibly embodying a program ofinstructions executable by said computer to perform a method ofdesigning an integrated circuit structure, said method comprising:receiving design parameters for an electrostatic discharge circuit and aspecified application frequency, wherein said electrostatic dischargecircuit comprises an electrostatic discharge device electricallyconnected in parallel to an inductor; generating a first design for saidelectrostatic discharge device based on said design parameters;determining, based on said first design, a capacitance value for saidelectrostatic discharge device; determining, based on said capacitancevalue and said application frequency, an inductance value for saidinductor to ensure that a subsequently designed inductor-capacitor (LC)circuit will have a resonant frequency at said application frequency;and generating a second design comprising said inductor with saidinductance value aligned over and electrically connected to saidelectrostatic discharge device of said first design to form saidinductor-capacitor circuit.
 10. The program storage device of claim 9,wherein said determining of said capacitance value comprises: accessinga table of capacitance values according to device sizes and types; anddetermining said capacitance value based on a type and size of saidelectrostatic discharge device as specified by said first design. 11.The program storage device of claim 9, wherein said generating of saidsecond design comprises selecting a diameter of a planar conductive coilfor said inductor, a shape of said coil, a number of turns in said coiland a length of said coil sufficient to achieve said inductance value.12. The program storage device of claim 9, wherein said receiving ofsaid design parameters comprises receiving a specified current density,and wherein said method further comprises: determining a minimum wirewidth for said inductor that is sufficient to sustain said specifiedcurrent density without failure; and generating said second design sothat said inductor has no less than said minimum wire width.
 13. Theprogram storage device of claim 9, wherein said generating of said firstdesign comprises generating said first design such that saidelectrostatic discharge device is wired to a first metal level abovesaid electrostatic discharge device, and wherein said generating of saidsecond design comprises generating said second design such that saidinductor comprises a planar conductive coil in a second metal levelabove and parallel to said first metal level and such that a first endof said coil is electrically connected to said first metal level by aconductor extending vertically from said first end to said first metallevel perpendicular to said inductor.
 14. The program storage device ofclaim 13, wherein said method further comprises generating a thirddesign comprising a shield in a third metal level between and parallelto said first metal level and said second metal level, and wherein saidshield is configured to minimize inductive coupling between saidinductor and said electrostatic discharge device of said second designand comprises an opening through which said conductor extendsperpendicular to said shield.
 15. A computer-aided design system fordesigning an integrated circuit, said system comprising: a userinterface for receiving design parameters for an electrostatic dischargecircuit and a specified application frequency, wherein saidelectrostatic discharge circuit comprises an electrostatic dischargedevice electrically connected in parallel to an inductor; and at leastone processor adapted to generate a first design for said electrostaticdischarge device based on said design parameters, wherein said processoris further adapted: to determine, based on said first design, acapacitance value for said electrostatic discharge device; to determine,based on said capacitance value and said application frequency, aninductance value for said inductor to ensure that a subsequentlydesigned inductor-capacitor (LC) circuit will have a resonant frequencyat said application frequency; and to generate a second designcomprising said inductor with said inductance value aligned over andelectrically connected to said electrostatic discharge device of saidfirst design to form said inductor-capacitor circuit.
 16. The designsystem of claim 15, further comprising a storage device comprising atable of capacitance values according to device sizes and types, whereinsaid first design comprises a type and size for said electrostaticdischarge device, and wherein said processor is further adapted toaccess said table in order to determine said capacitance value of saidelectrostatic discharge device based on said type and said size of saidelectrostatic discharge device.
 17. The design system of claim 15,wherein said processor is further adapted to determine said inductancevalue by solving for one over a product of a capacitance value of saidelectrostatic discharge device and said specified application frequencysquared.
 18. The design system of claim 15, wherein said processor isfurther adapted to generate said second design such that said inductorcomprises a planar conductive coil with a shape, a diameter, a number ofturns and a length sufficient to achieve said inductance value.
 19. Thedesign system of claim 15, wherein said design parameters comprise aspecified current density, and wherein said processor is further adaptedto determine a minimum wire width for said inductor that is sufficientto sustain said specified current density without failure and further togenerate said second design so that said inductor has no less than saidminimum wire width.
 20. The design system of claim 15, wherein saidprocessor is further adapted: to generate said first design such thatsaid electrostatic discharge device is wired to a first metal levelabove said electrostatic discharge device, and to generate said seconddesign such that said inductor comprises a planar conductive coil in asecond metal level above and parallel to said first metal level and suchthat a first end of said coil is electrically connected to said firstmetal level by a conductor extending vertically from said first end tosaid first metal level perpendicular to said inductor.